Changes in the New AASHTO Guide Specifications for Seismic Isolation Design (1997-1999)

In 1993, a project began at the University at Buffalo under the title “Longevity and Reliability of Sliding Seismic Isolation Systems” with the support of MCEER. The objectives of the project were then defined as the collection of laboratory and field data on the behavior of sliding bearings and the qualitative prediction of the long-term frictional properties of these bearings. In 1995, the author of this paper became involved in the development of the new AASHTO Guide Specifications for Seismic Isolation Design as a member of a task group of the T-3 Seismic Design Technical Committee of the AASHTO Bridge Committee. Specific challenges for the T-3 task group were the proposal of new response modification factors for bridge substructures and the justification thereof, and the development of a rational procedure for determining bounding values of isolator properties for analysis and design. Based on the needs of the T-3 task group, the objectives of the research project were modified to include the development of a procedure for establishing bounding values of isolator properties. Moreover, a new project began in 1996 at the University at Buffalo with the support of MCEER to develop appropriate response modification factors for the substructures of seismically isolated bridges. These efforts culminated in the establishment of the concept of System Property Modification Factors, the development of revised values for response modification factors, and the inclusion of both in the new AASHTO Guide Specifications, which were published in 1999 (American Association of Highway and Transportation Officials, 1999). Changes in the New AASHTO Guide Specifications for Seismic Isolation Design